Deep-level electron traps in vapor phase epitaxial GaAs grown with oxygen injection

The effect of oxygen injection on electron traps in undoped epitaxial GaAs grown in a chloride vapor phase epitaxy (VPE) system is studied using deep-level transient spectroscopy (DLTS). The trap concentrations determined from constant-capacitance DLTS agree well with those obtained from low- and high-temperature differential capacitance measurements. Layers grown with successively higher partial pressures of intentionally added oxygen each contain the same four electron traps typically observed in nonintentionally doped n-type VPE layers. Three of these traps are present in concentrations at or below the mid 1011-cm−3 range, while the dominant level known widely as EL2 remains constant at a concentration of (2.5±0.5)×1014 cm−3. However, no additional deep levels due to the oxygen are observed. Although the trap concentrations are independent of the oxygen injection, the amount of unintentional Si incorporated is reduced by almost three orders of magnitude resulting in a fourfold increase in 77-K electron mobility.